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Re: Powering Sony MZ-NH900 with 4.8 volts

Subject: Re: Powering Sony MZ-NH900 with 4.8 volts
From: "Adam Liberman" adam5532
Date: Sun Jan 21, 2007 1:27 pm ((PST))
Hi,

--- In  "Rich Peet" <> wrote:
> DC-DC converter in the normal primitive sense is a Voltage Regulation
> IC.  A common one is the LC7805 which is a 5 volt regulator.
...
> In recent years some manufacturers are getting smart and using this as
> an advertising plus. The SD722 recorder markets their recorder as
> being able to accept 10 to 18 volts. They likely are using a LC7805
> and allowed a 2X safty for voltage spikes and the like.

This is incorrect. A xx7805 is a IC linear regulator. A DC-DC
converter is completely different -- it is a switching regulator, and
contains various ICs and transistors as well as capacitors and
inductors. Sometimes all this is contained within a sealed module. A
linear regulator works by dropping the excess voltage as heat, so it
is wasted. A switching regulator turns on and off very rapidly
(usually 40KHz and up) to regulate the voltage, so it can be very
efficient (up to 93% or so), and wastes very little power as heat. The
trick in designing audio devices is to prevent any of the switching
noise from becoming audible.

Virtually all portable battery operated devices use switching
regulators in order to conserve battery life and reduce heat, and do
not use linear regulators like the 7805. When the SD722 says 10 - 18
volts, that is an absolute range. The switcher likely can not reduce
its duty cycle any further to regulate a higher voltage. In addition,
a higher voltage may exceed the maximum voltage and power ratings of
the semiconductors, inductors, and capacitors in the circuit and
damage the recorder. Some devices, like some cassette and minidisc
recorders, also use the unregulated battery voltage to power some
circuits, and exceeding the specified voltage range may destroy these
components.

On portable recorders that only specify one input voltage, like 6
Volts, it is likely they can tolerate a little more, like 6.4 (fresh
batteries) or 7.5 (unloaded unregulated power adapter). But without
analyzing the schematic for voltage and power ratings, and testing the
internal heat dissipation at various voltage levels and ambient
temperatures (which no-one is likely to go to the trouble to do), or
having input voltage specifications from the manufacturer, you should
keep the input voltage very close to the specified figure.

Thanks,
Adam






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